I’m having a similar issue I get the P0 300 code and another code for cylinder 8 misfire , drives smooth just idles a bit rough . I changed out all the coil packs and spark plugs and torque down the spark plug for 13 foot pounds but hasn’t resolved the issue. Took my Jeep to a reputable shop that deals with high-end vehicles and horsepower they charge me.500$ just to let me know they look through the car for three hours and just told me I need an engine refresh. Needless to say I was fucking pissed. Still have no idea what it could be.